The calibration and adjustment of sensors for driver assistance systems in a (motor) vehicle generally include determining the location of a surroundings sensor in relation to the chassis geometry or a defined vehicle coordinate system.
In the repair shop, for example, the location of a video camera for using driver assistance functions (e.g., for a warning when departing from the lane, detecting objects and the like) is to be recalibrated in relation to the chassis geometry after the camera has been installed or after major changes are made to the chassis. Radar sensors for automatic speed control, e.g., ACC (Adaptive Cruise Control), frequently must be mechanically adjusted to the chassis geometry, due to their narrow opening angle.
Examples of the calibration and adjustment of sensors for driver assistance systems are:                Testing and adjusting radar-based distance sensors (“Adaptive Cruise Control”)        Testing and adjusting infrared-based distance sensors (“lidar”)        Testing and calibrating rear view camera systems (“rear view”)        Testing and calibrating lane keeping camera systems (“lane departure warning”)        Testing and calibrating lane changing assistants (“blind spot detection”)        Infrared night view camera (“night view”)        Surroundings camera systems (“side view,” “top view”)        
The following requirements must be established to calibrate and adjust sensors for driver assistance systems:                Known chassis geometry for defining the vehicle coordinate system        Orienting a calibrating/adjusting means in the field of vision of the sensor to be calibrated/adjusted at a predefined position in relation to the chassis coordinate system        
To ensure a known chassis geometry and to reduce costs and complexity, calibrating and adjusting devices are often offered as add-ons to measuring devices for chassis measurement.
A method for calibrating a video camera sensor, which is described, for example, in German Patent Application No. DE 10 2008 042 018 A1, is described below by way of example with reference to FIG. 1. The relation between the coordinate systems described below for determining the chassis geometry is implemented with the aid of optical 3D measuring systems, as described by Steffen Abraham, Axel Wendt, Günter Nobis, Volker Uffenkamp and Stefan Schommer in Optische 3D-Messtechnik zur Fahrwerksvermessung in der Kfz-Werkstatt (3D Measuring Systems for Chassis Measurement in the Automotive Repair Shop), Oldenburger 3D-Tage, Wichmann Verlag, 2010.
To measure the chassis, wheel clamps 28, 30 are mounted on wheels 12, 14 of a vehicle 7, to which, in turn, wheel measuring panels (targets) 20, 22 having photogrammetric measuring marks are attached. A measuring head 32, 46 is situated on the left and right sides of vehicle 7. Each measuring head 32, 46 includes two stereo camera systems, each of which has two cameras 36, 38, 40, 42, 50, 52 54, 56 and one reference system 44, 58.
The geometry of cameras 36, 38, 40, 42, 50, 52 54, 56 of the two stereo camera systems of a measuring head 32, 46 is calibrated both intrinsically and extrinsically with regard to its relative orientation. The calibration makes it possible to determine the 3D coordinates of the measuring marks on wheel measuring panels 20, 22 within coordinate system XV (front) or XH (rear) of particular measuring head 32, 46 within a shared measuring head coordinate system XL (left) or XR (right). The wheel measuring panels 20, 22 used do not have to be high precision pass point panels having premeasured measuring points.
Provided that wheel measuring panels 20, 22 are attached to wheels 12, 14 in a mechanically stable manner, the 3D location of wheel axle 13 may be determined continuously in all four stereo camera systems 36, 38; 40, 42; 50, 52; 54, 56. Reference systems 44, 58 furthermore continuously measure the toe angle between measuring heads 32, 46 and the tilting of measuring heads 32, 46. This makes it possible to calculate the chassis variables, e.g., the toe and camber angles, as well as other variables of the chassis, such as the steering geometry, including the kingpin and caster angles. Geometric vehicle coordinate system XM is finally defined by vehicle longitudinal axis 64, which is predefined by the toe of rear wheels 12, 14 now being measured.
The goal of the calibration is to determine the location and orientation of the camera of a surroundings sensor 15 within coordinate system XM of vehicle 7. For this purpose, a calibrating/adjusting device 62 having known measuring mark positions is positioned in front of vehicle 7 at point XT-FIX.
For the calibration operation, calibrating/adjusting device 62 is monitored by the camera of surroundings sensor 15 of the driver assistance system. The image coordinates of measuring marks on calibrating/adjusting device 62 are measured by the driver assistance system. Absolute orientation XC of the camera in relation to calibrating/adjusting device XT-FIX is determined by a spatial resection. This optical measuring step is carried out by control unit 17 of the driver assistance system in vehicle 7. The calibration step is started via the diagnostic interface of control unit 17 in vehicle 7.
To be able to determine the installation angles (pitch, yaw and roll angles) and other parameters of the camera in relation to the chassis geometry, the position of calibrating/adjusting device XT-FIX within coordinate system XM of vehicle 7 is known to control unit 17 in vehicle 7. The software in control unit 17 requires that calibrating/adjusting device 62 be located at permanently defined position XT-FIX known to control unit 17. Only if this is the case will the installation angles ascertained by control unit 17 be correct.
The manual orientation of calibrating/adjusting device 62 to position XT-FIX is associated with a certain amount of time and requires extensive knowledge of the calibration operation on the part of the auto mechanic. An imprecisely oriented calibrating/adjusting device 62 results in accuracy losses during calibration and adjustment of the camera or surroundings sensor 15.